1. Field of the Invention
The present invention relates to tap tools, methods of forming threaded holes in sheet metal and workpieces, and in-die hole piercing/tapping processes, and more particularly, to a tool for and method of piercing, extruding, sealing, burnishing and forming a rolled thread in a single pass, wherein the tool and method are adapted for particular use with a hydroforming p rocess.
2. Discussion of Prior Art
Machine screws and threaded bolts have long been used to secure parts of an assembly. To enable this method of joining, tapping tools and processes have likewise been developed to cut or roll female threaded holes within a workpiece or part. In doing so, it is typical for a pilot hole to be initially formed in the workpiece, wherein the hole presents a diameter smaller than that of the intended bolt. A thread having the same pitch with that of the bolt is then perpendicularly rolled into the periphery of the pilot hole. More preferably, a shoulder is provided along the periphery so as to promote perpendicular engagement between the male bolt and female hole. Thus, at least a two-step tapping process is widely appreciated, wherein one set-up for piercing is required to be changed-out by another for tapping. Concernedly, however, this adds costs associated with increased production time, complexity, and repair/replacement.
Hydroforming has concurrently become an increasingly popular method of forming finished parts prior to tapping. This method of part production involves securing a workpiece within a die cavity, engaging the workpiece with pressurized fluid, and expanding the workpiece, so as to cause it to conform to the die cavity.
Accordingly, there is a need in the art for an improved tool or method of tapping a workpiece in a single pass, and more preferably, one that is compatible with and utilizes the advantages of the hydroforming process.